Manufacture of sulphuric acid by the contact process



Dec. 5, 1944. c. v. HERRMANN MANUFACTURE OF SULPHURIC ACID BY THE CONTACT PROCESS Filed March 21, 1942 0-04 UZOMPFW dummommju EDu O $30 530 $39 $62 w 28 @555 wzrQE 56 $35: NE 7 z zo mw zou mm: wwz Sz Carl KHL-rrmann ATTORNEY Patented Dec. 5, 19st; 2 35mm UNITED STATES. PATENT oFFi" MANUFACTURE OF SULPHURIC ACID BY THE CONTACT PROCESS Carl V. Herrmann. Wilmington, Del., assignor to E. I. du Pont de Nemours & Company, Wilmington, DeL, a corporation of Delaware Application March 21, 1942, Serial No; 435,671

4 Claims. (01. 23-175 This invention relates to the production of lowand thence to an oleum absorber and a 98 per lead strong acids in a contact sulphuric acid plant cent absorber.

- in which acids containing lead are taken into the Drying of the wet, cold burner gas is eii'ected plant and fortified to produce strong acids. by continuously circulating over each of the three It is common practice in the manufacture of 5 towers an acid of suitable drying strength, as sulphuric acid to operate a contact and a chamshown in each of the three circulating systems I, ber plant conjunctively. Acontact plant normally 2 and 3. Each of these circulating systems inis capable of producing excess $03 over that recludes a cooler 4, 5 and 6, in order that the acid.

quired to make sulphuric acid from the water which 'in passing through the drying tower benecessarily introduced in the process. Accordll comes hot by heat of dilution of the sulphuric ingly large quantities of S03 are available for -foracid, may be cooled. The acid circulated over tifying the weaker chamber acids. It is desirthe No. 3 drying tower is maintained at drying able to fortify such acids for in that manner the acid strength by dripping into the circulating sysproduction of strong acids, i. e., 98 per cent or tem chamber acid of 66 Baum strength while stronger, is greatly increased. The general use- 1: the strength of the No. 2 and No. l drying tower Iulness of such processes, however, is limited in acids are maintained, respectively, by dripping view of the high lead content of acids s0 prospent drying tower acid from the succeeding towduced. er. Thus, as drying acid accumulates in the cir- The processes heretofore available for removculating system 3 by dilution the make is withing lead from chamber acids have not been de- .0 drawn through line I and' dripped into the cirsirable or economical. It has. long been known culating system 2 where the drying tower acid that lead, in certain ranges of concentration at .is maintained at a lower strength because of the least, has a solubility proportional to the strength greater moisture content of the gas being dried of the acid. Hence, if the chamber acid is diinv that tower. Likewise, as the drying tower acid luted, lead sulphate is precipitated and may be in circulating system 2 increases in quantity by separated in settling tanks. The separation of dilution the surplus is drawn off through line 8 lead, however, in this manner can not be effected and dripped into the circulating system I where without sacrificing the capacity of the plant to the drying tower acid is maintained much weaker produce strong acid of oleum strength because the because of "the greater moisture content being water introduced to dilute the chamber acid prodried in that tower. As the drying acid circulatportionately reduces the capacity of the plant ing in circulating system I increases due to diluto produce strong acid. tion the surplus is drawn on. through line 9 into I have now discovered processes by which settling tank II]. There the lead sulphate which chamber sulphuric acid and like lead-containing has precipitated in dilution of the chamber acid lead'sulphate, andthe acid thus obtained utiacids'can be fortified in a contact sulphuric acid settled out and the supernatant relatively leadplant without sacrificing capacity to produce free acid is withdrawn through line ID to the 98 strong acid of oleum strength and without exper cent absorber where it is fortified to 98 per cessive co'ntaminationby lead compounds, in accent strength. The 98 per cent acid thus obcordance with which cold moisture-laden gas utivtained passes through the cooler ll, through lized in the production of S03 is scrubbed with 4( line l2 into, the oleum absorber where it is fortiextra-process lead-containing sulphuric acid of fled-to oleum strength. The acid thus obtained drying acid strength whereby moisture is transis relatively lead free.

ferred toand dilutes the extra-process acid, the The only water introduced into the system outextra-process acid treated to remove precipitated side of that contained in the chamber acid is that abstracted from the wet, cold burner gas in the lized-inthe absorptignmf the sulphur trioxide prodrying towers Nos. l, 2 and 3. The process is duced in the conved'siiin of the driedburner gas. v therefore operated on a minimum of water and The'invention maybe more fully understood-by. of consequence. produce maximum production reference to the accor'npanyingflow sheetfwhich of strong acid.

illustrates a typical embodiment of. the inven- Theefl'ectivenessotthe invention in removal tion. Wet, cold burner gas obtained from any or lead'is proportional to the dilution of chamsuitable wet purification system, not shown, is her acid efiected in the drying system and this passed through drying towers I, 2 and. 3, thence in turn is dependent upon the number of towers to any suitable conversion 'system involving preemployed and the moisture content of th burner heaters, converters, heat exchangers, coolers, etc., gas. In a wet purification process the burner gas is essentially saturated with moisture so that variation irom this source is mainly a function nomically practical to circulate acid over the,

No. l drying tower at a strength of 49 Baum (60.8%) and acid over the second drying tower purification is not employed but in which the air v of 62 Baum (81.3%), and over the No. 3 drying tower in acid of 65.5 Baum (90.6%), and obtain a proper distribution of the drying load among the three towers. If only two towers are employed a greater burden is imposed upon each, and of consequence the extent of dilution can not be so great. However, by using two, .three, four or, more towers any degree of dilution desired is possible.

The principal object of the invention, namely, the reduction of lead content in the strong acids, is accomplished in some measure by any degree of dilution, but for most purposes for which leadfree strong acid is in demand it is desirable to eilect a dilution .to about 46 to 58 Baum (56.5 to 74.4%) and this is most conveniently eiIected in a three-tower system asillustrated.

While I have illustrated my invention with reference to .the fortification of chamber acid of 66 Baum it will be understood .that with slight modification it may be practiced in the concentration of extra-process lead-containing acids of other strengths, for .example, chamber acid of 60 Baurn. These two strength acids are the common strengths produced in lead chamber systems, the 66 Baum being the highest concentration practically obtainable in systems having a high heat content and heat economy. It will be understood also'that the particular drying acid of theNo. 3 drying tower would then be returned to the 98 per cent absorber in accordance known in the art. Also, with slight variation the lead-containing acid maybe dripped into any or all of the circulating circuits.

In a contact system devoted essentially to the production of strong acid of. oleumstrength, the 98 per cent absorber may be operated chiefly as a clean-up absorber, in whichcase 'it might be desirable to feed all or a portion of the purifled chamber acid directly to the oleum absorber, or oleum absorbers if more than one is employed. Also, should the moisture in the gas be insumcient to provide the water necessary for operating the 98 per cent absorber the deficiency maybe made .up by dripping water or lead-free acid from any suitable source.

It will also be understood amt. invention.

in its broader aspects is applicable to the socalled abbreviated contact systems, in which wet utilized in burning sulphur is pre-dried. The amount of dilution which can be effected in such a process, however, is limited in viewoi. the relatively low moisture content of the air being dried. The invention while thus applicable to other systems is most useful in connection with the wet purification system where almost any degree of dilution desired may be eiIected and where a practical degree of dilution such as will produce an acid suiiiciently free of lead for practical purposes can be obtained without increasmg the equipment or cost.

Within the scope of the appended claims these and other variations may be made without de-.

parting from the spirit of the invention.

I claim:

1. In the manufacture of sulphuric acid by the contact processin which moisture laden gas utilized in the production of the sulphur trioxide is dried, the steps of drying said gas by contact with extra-process lead-containing sulphuric acid of drying strength, said drying efiecting suflicient dilution to cause precipitation of lead sulphate, producing sulphur trioxide from said gas, separating precipitates from the spent drying acid and absorbing sulphur trioxide in the acid thus obtained from the spent drying acid.

2. In the manufacture of sulphuric acid by the contact process in which cold moisture saturated burner gas is dried prior to conversion to sulphur trioxide and absorption, the steps of drying said burner .gas with extra-process leadcontaining sulphuric acid of drying strength whereby moisture'is transferred to and dilutes the extra-process acid and converting the dried burner gas to sulphur trioxide, treating the thus diluted extra-process acid to separate precipitates and then fortifying it by absorbing sulphur trioxide fromthe conversion gases.

3. In the manufacture of sulphuric acid by the contact process the steps of subjecting burner gas to wet purification, drying the cold, wet burner gas in a plurality of drying towers over which there is dripped sulphuric acid of drying strength obtained from a lead chamber process and producing sulphur trioxide from the dried burner 'with the principles and practices commonly' gas, withdrawing the spent drying acid into a settling tank and permitting precipitated lead sulphate to separate out, withdrawing the supernatant acid and fortifying it by absorption of sulphur trioxide produced in the process.

4. In the manufacture of sulphuric acid by the contact process in which moisture laden gas utilizedin the production of the sulphur trioxide is dried, the stepsoi drying said gas by contact with extra-process lead-containing sulphuric acid CARL V. HERRMANN. 

